Fluorspar-flux additive in a coking operation



United States Patent ABSTRACT OF THE DISCLOSURE Self-fluxing coke is produced by a process of mixed crushed coal with fluorspar and then pyrolyzing the mixture by destructive distillation. The resulting coke is stronger and has the fluorspar intimately associated with the ash content of the coke. The fluorspar acts as a flux for the ash during combustion of the coke.

This invention relates to the destructive distillation of coal for purposes of obtaining coke and, more particularly,

to an improved coking operation capable of producing stronger coke.

Coke is the product obtained by strongly heating coal out of contact with the air until the volatile constituents are driven off. This process can also be described as the destructive distillation of coal or its ca-rbonization or pyrolysis. Coke consists essentially of carbon together with the incombustible matters or ash contained in the coal from which it is derived. Other constituents in minor quantities and traces are present but for purposes of the present invention, these particular areas need not be further explored. Coke is essentially a partially graphitized carbon, its density being about midway between that of coal and graphite; and an essentially spongy structure is established by the escaping gases during the coking operation. It is this combination of properties that gives it its chief value in iron smelting, the substance being sufficiently dense to resist oxidation by carbon dioxide in the higher regions of the furnace, while the vesicular structure provides an extended surface for the action of heated air and facilitates rapid consumption at the tuyeres.

However, one of the most deleterious constituents of coke is ash. In this connection, it is now customary to crush and wash the coal rather carefully to remove intermingled particles of shale and dirt before coking so that the ash content is maintained at a minimum. Usually 10% is not exceeded where possible and a fair average for good coke would be in the neighborhood of about 8% ash.

The coking art recognizes several methods of manufacture described and illustrated in the literature in considerable detail. These methods typified by the ovens employed include among others By-Product Coking, Beehive Coking and Gas Retort Coking. Suflice it to say that in this country, two or more kinds of coal are frequently mixed for By-Product Coking, for example. This mixture is pulverized or finely crushed until a major proportion ordinarily about 75%, passes an /s" screen. It is found to be advantageous to add small amounts of low volatile coal sometimes referred to as semi-bituminous coal, to the high volatile coals that constitute the primary charge in order to obtain optimum metallurgical cokes. The coke is quenched following removal from the oven battery at a station a relatively short distance away. The car containing the hot coke is quickly removed from the oven to the quenching station at which it is quenched with a carefully controlled amount of water, following which it is subjected to further cooling and drying. Instead of water an inert gas is oftentimes employed for purposes of cooling the coke. This procedure is termed dry quenchmg.

The ash contents of coke recognizably reduces the heat capabilities of the coke. Ash has proven to be extremely difficult to fuse in iron blast furnaces as well as other blast furnaces. In order to circumvent this undesirable effect, furnaces of this nature have been adopted to flux the ash in order to convert it into an easily fusible glass or lava-like substance called slag. The formation of this slag is ordinarily induced through the incorporation of a fluxing agent into the furnace but this procedure, nevertheless, has its limitations. The primary problem is to deploy the flux in such a manner that it may effectively act upon the ash that serves to hamper the generation of optimum heat. The prior art attempts at minimizing the effects of the ash have been successful only to a limited extent and much room for improvement in the rapidity and extent of slag formation remains.

In normal practice in iron and steel furnaces, it has been found that the ash interferes rather significantly with the oxidation of the carbon of the coke. As will be appreciated, the capacity of furnaces of this nature is limited by the pounds of coke that is capable of being oxidized per unit of time. Coke is generally a hard, sponge-like cellular material composed primarily of carbon, ash and other constituents including those of volatile nature. This ash content is distributed in the Walls of the cells of the coke generally in a somewhat uniform pattern. When the coke is ignited in oxygen supplied to it, the carbon of the coke combines with the oxygen. As the carbon of the coke is oxidized, the refractory ash content in the oxidized portion of the coke is in part left behind on the surface of the as yet unoxidized carbon and also interferes physically with the process of oxidation.

The rapidity in which the carbon of the coke can be made to combine with the oxygen supplied for this purpose is a major factor in the capacity of the furnaces. It is with respect to the optimization of the rate of oxidation of the coke to heretofore unrealized high levels that this invention is particularly directed.

It is, therefore, a principal object of this invention to increase the level of oxidation of the carbon of the coke in order to optimize the generated heat capabilities of coke by increasing the extent and degree as well as rapidity of slag formation by having a flux intimately associated with the ash of the coke such that the ash may be readily and most expeditiously converted into the slag.

Another object is to incorporate a flux of this nature into the coke during the coking operation, this flux preferably being in the nature of finely powdered granulated fiuorspar of substantially chemically pure form.

In this manner, the present invention proposes to flux the greater part, if not all, of the coke ash; and particularly to permit it to be fluxed as fast as it is liberated on the surface of the coke. In this manner, the coke ash is rapidly removed from the surface of the coke to thereby present a relatively clean surface upon which the oxygen supply in the furnace is capable of oxidizing the carbon of the coke without hindrance. Where needed, the conventionally employed fluxing techniques in these furnaces can also supplement the fluxing technique proposed by this invention. Accordingly, the carbon of the coke is adapted to be oxidized at an accelerated rate.

Thus, the present invention incorporates finely powdered or granulated fluorspar, in measured amounts, along with the coal prior to or even at the same time that it is introduced into the coking oven. Under these circumstances, the fluorspar will be thoroughly mixed and rather intimate with the ash of the coke. Upon incorporation into an iron or steel furnace, the coke ash will be fluxed and rapidly fused and readily removed from the zone of combustion.

It has been found that the addition of fiuorspar concentrate to the coal before it is coked does not weaken nor hurt the coke in any way and, in fact, gives rise to a stronger coke. A self-fiuxing coke is, accordingly, produced which eliminates the need for storage bins, feeders and any other equipment necessary for the injection of fiuorspar into blast furnaces. This flux already contained in the coke would simply work its beneficial results with no effort at all by the furnace operator. To some extent, following the coking operation, the fiuorspar has fiuxed the ash in the coke. In any event, it does combine with the ash for purposes of forming a more fusible ash in the coke. In actual practice, it has been observed that the relationship of the fiuorspar with the coke, following the coking operation, is in essence the same as the ash in the coke, namely, uniformly distributed throughout the coke. The coke is slightly stronger due to the incipient fusion of the ash caused by the presence of the fiuorspar flux.

The present invention preferably employs dry acid grade fiuorspar in substantially pure form having a minimum of 97% CaF This grade and quality of fiuorspar is preferred for the process of this invention inasmuch as readily obtainable on the market and also in finely ground state of substantially uniform quality. It should be understood, however, that this invention is not limited to the specified analysis of CaF since other grades of fiuorspar, for example, metallurgical grade would be usable with satisfactory results, if finely ground. By finely ground fiuorspar, the present invention preferably employs 100% minus 100 mesh Tyler Screen size. It should be understood, however, that this invention is not limited to this particular maximum size inasmuch as coarser material can be used beneficially but with decreasing effectiveness as the particle size becomes larger or coarser.

It has been found that an optimum value of the fluorspar added calculated against the ash content of the ultimately produced coke should preferably be in the neighborhood of about 8 to 10%. This has been found to provide a reasonably effective working range in obtaining the desired increased rate of coke combustion, with the preferred percentage being about 10% fiuorspar calculated against the ash content. Below this specified range, less and less beneficial results are obtained. Above 10%. benefit is obtained but cost and other variables including possible waste of fiuorspar are major factors. In this connection, the fiuorspar should not exceed in any case 4% by weight of the coke.

An actual and exemplary By-Product Coking procedure in accordance with this invention utilized an average size lay-product coke oven having a capacity of about 12 tons of coal. A mixture of 80% Pittsburgh and Pocahontas coal (dry basis) was transferred, crushed, and screened according to usual practice. Based on a percentage yield of 72% coke calculated for this particular mixture according to actual production runs, of which 8% was calculated to be ash, approximately 0.57 pound of fiuorspar per hundred pounds of coal was introduced. The coal and fiuorspar were intimately mixed and then charged into a hot empty oven. The coal and fiuorspar mixture was then chemically transformed into coke and volatiles by pyrolysis. In this connection, a typical By-Product Coking procedure employs a battery of to 90 or more ovens. These ovens and their specifications are well known in the art and disclosed in considerable detail in the literature. The individual by-product coke ovens are intermittent in their operation with each oven started and finished at different times so that the operation of the entire battery is in a relatively orderly manner. The finely crushed coal mixture and fiuorspar are charged into the oven by dropping from a lorry car through charging holes provided for such purpose in the oven. The charge is dropped in the top in that part of the oven were the oven walls are approximately at 2000 F. The heating of the coal is carried on in the usual manner and the charge left in the oven until it is completely coked, and the evolution of the volatile matter has ceased. The average temperature at the center of the charge at the end of the heating period is usually about 1800 F. while the average fiue temperature is about 2350 F. The temperatures as will be appreciated by those skilled in the art vary with the conditions of operation, the coking time, the dimensions of the oven, the kind of coal, its moisture content and fineness of division.

At the end of the coking time, the doors on the discharge end of the oven were open and the entire red hot matter pushed out into a quenching car which was then transferred to a quenching station where the hot coke was sprayed with water ordinarily about 6000 gallons per twelve ton oven charge. In accordance with usual practice, the car was thereafter drained and the coke transported to a crushing and screening plant. The coke produced in accordance with this procedure was analyzed and determined that the fiuorspar was intimately mixed with the ash of the coke. Upon employment of this coke in an iron blast furnace, it was observed that the rate of coke combustion was increased and the production of this furnace noticeably increased compared to production runs not employing a flux in the furnace as well as production runs incorporating fiuorspar into the furnace in accordance with usual practice in amounts substantially equal to that added to the coal prior to the coking operation.

A similar by-product coke oven procedure was run in which bituminous coal was utilized. Based on a production of 1400 pounds of coke per ton of coal and a coke ash content of 10% about 10 fiuorspar was added to the coal calculated against the ash content of the coke or, in other words, 1.4 pounds of fiuorspar were added to each ton of coal. Again, the rate of combustion of coke produced in accordance with this procedure in an iron blast furnace was significantly increased compared to that utilizing ordinary coke obtained by a similar procedure without having fiuorspar incorporated therein that was fiuxed by the incorporation of fiuorspar directly into the furnace in accordance with conventional techniques.

With respect to both of the above exemplary production runs, in accordance with the teachings of this invention, the percentage of fiuorspar to ash content was decreased with the observation that the extent of fusing of the ash during the operation of the iron blast furnace and production of the slag was proportionately decreased with the noticeable rate of coke combustion likewise decreased. With fluorspar percentages increased above 10% of that calculated against the ash content of the coke, beneficial results were definitely detected but it was observed that the rate of coke combustion was not significantly larger than with 10% indicating a definite wastage which increased with the increase in percentage about 10%.

Thus, among others, the several aforenoted objects and advantages are most effectively attained. Those somewhat several preferred exemplary embodiments have been disclosed and described in detail herein and it should be understood that this invention is in no sense limited thereby, but its scope is to be determined by that of the appended claims.

I claim.

1. A method of producing self-fiuxing coke comprising mixing crushed coal and fiuorspar together in accordance with predetermined proportions, pyrolyz-ing the mixture by destructively disilling the coal at elevated temperatures until the evolution of volatile matter has reached a predetermined level to thereby obtain a stronger coke having a certain ash content with fiuorspar intimately associated with the ash, whereby the fiuorspar acts as a fiux for the ash during combustion of the coke.

2. A method of producing self-fluxing coke comprising providing a crushed screened coal and finely divided fluorspar, mixing the coal and flu-orspar in accordance with predetermined proportions, pyrolyzing the mixture in a coking oven to chemically transform the coal to coke having a certain ash content, removing the hot mixture from the oven, quenching the hot mixture and then transporting the mixture for further processing to provide a stronger coke having fiuorspar intimately associated with the ash of the coke, whereby the fluorspar acts as a flux for the ash during combustion of the coke.

3. The invention in accordance with claim 2 wherein the size of the particles of the fluorspar is no more than that capable of passing through the minus 100 mesh Tyler Screen.

4. The invention in accordance with claim 2 wherein the fiuorspar is dry acid grade fiuorspar having a mini- 5 7. The invention in accordance with claim 2 wherein the fiuorspar is present in an amount of about 10% by weight of the ash.

References Cited UNITED STATES PATENTS 98,606 1/1870 Lynd 20120 282,440 7/1883 Cooper 201-2O 1,959,182 5/1934 Tyrer 20l39 XR 2,823,112 2/1958 Miller 75-94 FOREIGN PATENTS 1,074,005 1/ 1960 Germany.

WILBUR L. BASCOMB, IR., Primary Examiner. D. EDWARDS, Assistant Examiner.

U.S.CI.XJR. 

